1. Field of the Invention
This invention relates to electronic circuits, and more particularly to devices for electronically controlling display devices to realistically simulate certain navigational equipment such as Radar and Sonar.
2. Description of the Prior Art
The increased traffic in the air and on the sea has caused an increase in the number of air and marine collisions. In addition to the loss of life and human hardships, property losses have been great. Reasons for such collisions are many and complex, but one of the most important of these is the lack of proper use of radar and sonar systems.
Radar and sonar systems produce signals which have the capability of penetrating fog, darkness, rain, haze, and locating objects which are a great distance from the source that generated the signals. Radar detection of an object is achieved by transmitting a beam of radio-frequency (rf) energy and detecting the energy reflected by the object. A small part of the rf energy is reflected by the object back to a sensor located near the transmitter. Radar ranging is accomplished by timing the period required for the rf energy to make the round trip from the detected object to the transmitter. The distance to the detected object is equal to one-half the time elapsed for the rf energy to make the round trip times the velocity of the rf energy. Sonar detection is similar to radar detection; however, acoustic radiation is the energy radiated rather than rf.
Modern airplane and ship navigation techniques depend on the use of radar and sonar systems. Thus, training in their use is essential for safe and efficient airplane and ship operations.
Man has invented simulators and other training devices to teach students how to use and operate various types of equipment without undergoing the dangers that are inherent in the equipment's actual operation. It is a great deal safer for an air traffic controller to learn how to control the landing and take-off patterns of aircraft in a simulator on the ground that at an actual radar display in the control tower.
One method used in the prior art to simulate radar and sonar displays was to utilize a digital computer for the supplying of information that would be outputted to a plurality of displays. The computer must have sufficient computational speed in order to perform all of the necessary computations that must be performed during a sweep of display and the computer's memory must be sufficiently large to contain all of the information regarding the geographical area that is being simulated. Information pertaining to the simulated geographic area is entered into a computer in X, Y (rectangular coordinate) format and stored in the computer's memory in the form of a table. It is often convenient to enter geographic information in the computer memory in rectangular coordinates, since this is the manner in which geographic information is usually given, i.e., in latitude and longitude. However, the geographic information displayed on the CRT display, using a Plan Position Indicator format sweep, is in polar coordinates. Therefore, it becomes necessary for the computer to convert the geographic information from rectangular to polar coordinates. The table also holds the results of the computer's conversions of the X. Y formatted data into .rho. (rho), .theta. (theta) formatted data. The expression for the conversion of the X position data is .rho. sin.theta., and the expression for the conversion of the Y position data is .rho. cos.theta.. In the aforementioned expressions, rho represents the range and theta represents the bearing. This conversion must constantly take place as the antenna pointing vector moves around or sweeps the display.
The computer must process the X, Y data and convert it into a rho, theta format. The information had to be range ordered, i.e., put in the proper sequential order for a particular bearing of the antenna at a given instant in time. Then the information would be outputted to external hardware buffers as range ordered data for that particular antenna position. The buffer's contents were compared to the instantaneous range sweep and when coincidence occurred, the buffers contents were fed to the CRT and displayed on a CRT in a Plan Position Indicator format. This procedure was very time consuming and required the computer to expend a great deal of time to process the information. The scan conversion can also be performed by a cathode ray tube with an electrostatic charge plane where the phosphor of a common viewing type CRT is generally placed. The CRT beam is thus writing in one format and then reading in another format.
In order to produce a realistic display, the appearance of the geographic area must change as the simulated vehicle moves. This geographical information must be continually updated by the computer as time elapses and the updating must take into consideration the speed and heading of the vehicle, the prevailing sea currents, the prevailing winds and movements of other vehicles, etc. From the newly computed information, video signals are generated to produce the proper information on the CRT displays.